M01_MOTO0256_00_SE_P08

A8 ENGINEPERFORMANCECHAPTER ONE

General Engine Diagnosis and Repair

CHAPTER TWO

Ignition System Diagnosis and Repair

CHAPTER THREE

Fuel, Air Induction, and ExhaustSystems Diagnosis and Repair

CHAPTER FOUR

Emission Control Systems Diagnosis and Repair

CHAPTER FIVE

Computerized Engine Control Diagnosis and Repair (IncludingOBD II)

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CHAPTER OBJECTIVES The technician will complete the ASE task list on General

Engine Diagnosis and Repair. The technician will be able to answer 12 questions dealing

with the General Engine Diagnosis and Repair section of theA8 ASE Test.

Poor engine performance can be the result of a long list ofproblems. Performance or driveability problems may be indi-cated by customer complaints of no starting, hard starting, lossof power, poor fuel mileage, engine knock, or engine misfire.Begin diagnosis by getting specific information from the cus-tomer. Find out the exact nature of the problem, under whatconditions it occurs, and when the symptoms first started.

CUSTOMER INTERVIEWThis first step in the process is crucial to diagnosing automotiveconcerns as it helps you get a clear understanding of the situa-tion. Use the following procedures to begin every diagnosis:

Verify the concern Research the history of the concern Ask the customer what they think the problem is Verify the information you have gathered

One of the most important steps in diagnosis is to verify thecustomers concern. Often a drivers description lacks some ofthe information necessary to begin proper diagnosis. Youmight misunderstand the drivers description or the symptommay be caused by circumstances that you might not encounterduring a typical operation check or test drive.

The best solution is for the driver to demonstrate theproblem for you or the service advisor. If that is not practical,question the driver about exactly when the problem occurs.This information can lead you to drive the vehicle under thesame conditions, and with an operational check, you can verifythe concern and begin to move to the proper subsystem tobegin your diagnosis.

A rational diagnostic procedure must be followed to suc-cessfully diagnose a customers complaint. By following logicalprocedures you can use your time more efficiently and replaceor repair the right components. Improper diagnosis leads tocome-backs, dissatisfied customers, and a waste of your timeand your customers time.

Before attempting to repair a performance problem, makesure the engine is in sound mechanical condition. In addition tointernal engine defects, driveability problems may be caused bya malfunction in the electrical, fuel, ignition, or emission control

systems. Accurate troubleshooting information for the vehiclebeing serviced is essential for testing and evaluating all systems.

After determining that there is a driveability problem, takea systematic approach to solving it. Work in a logical mannerto not only repair the problem, but also eliminate any otherconditions that may have contributed to the failure. To diag-nose performance problems, follow these four steps:

Preliminary inspection Road test Review vehicle service history and applicable support

materials Comprehensive engine testing

PRELIMINARY INSPECTIONEliminate any obvious problems by performing an under-hood inspection. The source of noise or vibration complaintswill often be revealed by a visual inspection. Problems such asrough running or stalling may be caused by a broken or dis-connected vacuum hose or electrical wire. When performingan inspection, check for the following:

Drive belts that are properly tensioned and free of cracks,frayed edges, and glazing

Electrical connections that are secure and clean. Inspectharnesses for signs of brittle insulation, rubbing, and bro-ken or damaged wires

Engine-mounted accessories that are properly supported;look for loose or missing bolts, worn bushings, and looseor broken support brackets

Engine mounts, torque struts, and vibration dampers thatare in good condition and securely attached

Hoses, water and vacuum, that are tight and properlyrouted. Replace any that are loose, brittle, kinked, broken,or otherwise damaged

Fuel lines, hoses, and fittings that are free of leakage anddamage

Battery, cables, and connections that are tight and free ofcorrosion. Also, check the battery electrolyte level andstate-of-charge

Secondary ignition cables, as well as the distributor capand coils, that are free of cracks, insulation damage, cor-rosion, and loose connections

Air filter element and ductwork that are clear and able tosupply a good flow of unrestricted air

Emission control system components that are properlyinstalled and connected. Repair any brittle, burned, ordamaged hoses and loose fittings

CHAPTER ONE

GENERAL ENGINE DIAGNOSIS AND REPAIR

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Chapter One: General Engine Diagnosis and Repair 495

Also look the engine over for any signs of leakage. Verifycoolant leaks by pressure testing the cooling system. Check thelevel of the engine oil and coolant, and look for indications ofdilution and contamination. Oil dilution is generally caused byraw fuel entering the crankcase. Look for a high fluid level andthin consistency accompanied by the odor of gasoline. Coolantleaking into the crankcase mixes with the oil to create a milky,brown-colored emulsion. Either condition, dilution or coolantcontamination, indicates internal engine problems.

Start the engine and allow it to idle while listening for anyunusual noises. A stethoscope is a handy tool for isolating top-end and bottom-end engine noises. To isolate difficult noises,connect a timing light and listen. Bottom-end noise will cyclein time with the flashing of the light. Top-end sounds will beaudible with every other flash of the light.

While the engine is running, check the exhaust for indi-cations of internal engine problems. Check for:

Black smoke. This is caused by a rich air-fuel ratio, andis often accompanied by the rotten egg smell of an over-worked catalytic converter

Blue smoke. This indicates excessive oil burning and oftengives off a pungent odor

Cloudy white exhaust. This is often the result of enginecoolant leaking into the combustion chamber. Burningcoolant also produces a distinctive chemical odor. Checkthe temperature gauge for overheating

Listen closely to the sound of the exhaust system. Be espe-cially conscious of irregular pulses or whistling soundsthat may indicate valve problems or a restricted exhaust

If everything looks good and there are no obvious problems,the vehicle is ready for a road test.

ROAD TESTWhenever possible, let the customer accompany you on theroad test. The customer knows the vehicle and can point outabnormal sounds, vibrations, and other annoyances thatmight be overlooked or considered normal.

Conduct a thorough road test; one quick lap around theblock is not enough. The engine must be brought to normaloperating temperature, and the test drive should include astop-and-go city driving cycle and a period of cruising at high-way speed. Proper road testing is extremely important forvehicles equipped with onboard diagnostics. An incompletetest may not record all of the intermittent, or soft, fault codes.A complete road test should take about 15 minutes. If possible,use the same route for all tests so that performance can becompared before and after service, as well as to the perfor-mance of similar vehicles. If a dynamometer is available, use itto simulate the road test.

When a problem occurs while driving, note the operatingconditions. Modulate engine and road speed to help isolatethe symptoms. Use the nature of the problem to determinewhich diagnostic tests to perform. The tests, and the order inwhich they are performed, depend on if the suspected prob-lem is in the:

Electrical or electronic system Internal engine

Ignition system Fuel system Emission control system

VEHICLE SERVICE INFORMATIONResource materials should be readily available when perform-ing diagnostic procedures. Resource materials and informationshould include:

Service History Service Manuals Diagnostic Manuals Wiring Diagrams Technical Service Bulletins Online Technical Support

The vehicle service history may be found in various ways. Askthe customer if they have copies of repair orders for previousservice work. OEM warranty systems track all repairs com-pleted under warranty and provide good details of the prob-lems serviced in the past.

Every vehicle has a specific Service Manual. These manu-als contain general service information, and often specific diagnostic and troubleshooting procedures for each systemwithin the vehicle, such as the emission or fuel system.

Most manufacturers also provide some type of Diagnos-tic Manual for the vehicle or vehicle family. Typically thesemanuals are for specific automotive systems such as electrical,fuel injection, and emissions/performance.

These manuals are more in-depth than Service Manualsas they provide component descriptions and operation theoryalong with the applicable troubleshooting procedures.

Some manufacturers dedicate separate publications forwiring diagrams rather than include them in the other manu-als. Either way, the wiring diagrams or schematics are requiredfor making most every electrical or electronic repair through-out the vehicle.

Technical Service Bulletins (TSBs) cover informationdiscovered after the Service and/or Diagnostic Manuals wereprinted, figure 1-1. Always consult TSBs for information aboutknown vehicle concerns or improvements for the most up-to-date information available.

Today there are several online technical support servicesthat compile repair information and TSBs for many vehicles.There is a nominal charge to access these services; however,many times the benefit far outweighs the cost.

SERVICE PRECAUTIONS AND WARNINGSCautions and WarningsThe diagnosis and repair procedures in the vehicle ServiceManuals generally contain both general and specific cautionsand/or warnings. The information is placed at strategic loca-tions throughout most Service Manuals and is designed to pre-vent the following from occurring:

Serious bodily injury to the technician Serious bodily injury to the driver and/or passenger(s)

of the vehicle, if the vehicle has been improperlyrepaired

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496 Chapter One: General Engine Diagnosis and Repair

Some manuals will contain more cautions and/or warnings,while others may have few included. Following are a few ex-amples of the cautions or warnings you may see.

Battery Disconnect CautionBefore servicing any electrical component, the ignition keymust be in the OFF or LOCK position and all electrical loadsmust be OFF, unless instructed otherwise in these proce-dures. If a tool or equipment could easily come in contactwith a live exposed electrical terminal, also disconnect the

negative battery cable. Failure to follow these precautionsmay cause personal injury and/or damage to the vehicle or itscomponents.

Fuel and EVAP Pipe CautionIn order to reduce the risk of fire and personal injury, observethe following items:

Replace all nylon fuel pipes that are nicked, scratched, ordamaged during installation. Do not attempt to repair thesections of the nylon fuel pipes

TechnicalService

Bulletin

SUBJECT: Sags/Hesitation/Stumble/Start & Stall

OVERVIEW: This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software (calibration changes).

MODELS: 2003 Minivan and Truck

NOTE: THIS INFORMATION APPLIES TO VEHICLES EQUIPPED WITH A 3.34L ENGINE.

SYMPTOM/CONDITION: Sags/Hesitation/Stumble or Start & Stall after a cold start in ambient temperatures of -7 - 30 C (20 - 86 F). The sag/hesitation or stumble may persist for up to a minute into a drive cycle and is attributed to high driveability index (Dl) fuel.

DIAGNOSIS: Using the Diagnostic System and or a Diagnostic Scan Tool with the appropriate Diagnostic Procedures Manual, verify all engine/transmission systems are functioning as designed. If Diagnostic Trouble Codes (DTC's) are present, record them on the repair order and repair as necessary before proceeding further with this bulletin. If no DTC's are present and the customer has described the above symptoms, perform the Repair Procedure. NOTE: WHENEVER A POWERTRAIN CONTROL MODULE (PCM) IS REPLACED DUE TO FAILURE, THE SOFTWARE OF THE REPLACEMENT CONTROLLER MUST BE VERIFIED FOR THE LATEST REVISION LEVEL. USE THE FLASH PROCEDURE TO UPDATE REPLACED CONTROLLERS AS NECESSARY.

PARTS REQUIRED: 1 14465020 Label, Authorized Software Update 1 54266086 Label, Authorized Modification

Fig. 1-1. Typical TSB.


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Do not hammer directly on the fuel harness body clips wheninstalling new fuel pipes. Damage to the nylon pipes mayresult in a fuel leak. Always cover nylon vapor pipes witha wet towel before using a torch near them

Apply a few drops of clean engine oil to the male pipe endsbefore connecting fuel pipe fittings. This will ensure prop-er reconnection and prevent a possible fuel leak

Fuel Gauge Leak CautionWrap a shop towel around the fuel pressure connection in orderto reduce the risk of fire and personal injury. The towel willabsorb any fuel leakage that occurs during the connection of thefuel pressure gauge. Place the towel in an approved containerwhen the connection of the fuel pressure gauge is complete.

Relieving Fuel Pressure CautionRelieve the fuel system pressure before servicing fuel systemcomponents in order to reduce the risk of fire and personalinjury. After relieving the system pressure, a small amount offuel may be released when servicing the fuel lines or connec-tions. In order to reduce the chance of personal injury, coverthe regulator and the fuel line fittings with a shop towel beforedisconnecting. This will catch any fuel that may leak out.

Handling ESD Sensitive Parts NoticeElectrostatic discharge (ESD) can damage many solid-stateelectrical components. ESD susceptible components may ormay not be labeled with the ESD symbol. Handle all electricalcomponents carefully. Use the following precautions in orderto avoid ESD damage:

Touch a metal ground point in order to remove your bodysstatic charge before servicing any electronic component

Do not touch exposed terminals. Terminals may connectto circuits susceptible to ESD damage

Do not allow tools to contact exposed terminals when ser-vicing connectors

Do not remove components from their protective pack-aging until necessary

Avoid the following actions unless required by the diagnosticprocedure:

Jumpering or grounding of the components or connectors Connecting test equipment probes to components or con-

nectors Connect the ground lead first when using test probes Ground the protective packaging of any component

before opening Resting solid-state components on metal workbenches, or

on top of TVs, radios, or other electrical devices

Ignition OFF When Disconnecting BatteryAlways turn the ignition OFF when connecting or disconnect-ing battery cables, battery chargers, or jumper cables. Failingto do so may damage the Powertrain Control Module (PCM)or other electronic components.

Electric Coolant Fan CautionAn electric fan under the hood can start up even when the en-gine is not running and can injure you. Keep hands, clothing,and tools away from any underhood electric fan.

COMPREHENSIVE ENGINE TESTINGIt is important to follow instructions from both the vehicle andthe test equipment manufacturers when performing enginetests. Some tests require the ignition to be disabled while thestarter motor cranks the engine.

Others may require bypassing the fuel pump relay, idlespeed controller, or some other electrical or electronic compo-nent. The proper test equipment, and the knowledge to use itcorrectly, are essential.

The following are general guidelines for performing com-prehensive engine tests. For some tests, more detailed proce-dures can be found in other books in this series. The tests hereare not presented in any specific order. The sequence in whichthey are performed will vary.

Unusual Engine NoisesEngine noises can be divided into two general catergories:those that originate in the top end of the engine, and thosethat originate in the bottom end of the engine. Begin enginenoise diagnosis by determining where in the engine the noiseis coming from. Bottom end, or crankcase, noises occur atcrankshaft speed, so they tend to produce a high-frequencyknock or rumble. Top end, or valve train, noises occur at alower frequency because these parts operate at one-halfcrankshaft speed.

A stethoscope is a handy tool for isolating noises. You canalso use a timing light to determine whether a noise is from thetop or bottom end of the engine. Connect the timing light andlisten. If the engine noise cycles in time with the flashing light,the sound is coming from the bottom end. Sounds that are au-dible with every other flash of the timing light originate in thetop end of the engine.

Top-End NoisesThe top end of a healthy engine produces a high pitched,whirring noise with a very rapid and much fainter sewing machinelike clicking coming from the valves. The more valvesthe engine has and the higher the idle speed, the more the in-dividual clicks will blend into a consistent drone. Any devia-tion is abnormal and indicates a problem. Listen for:

An irregular clacking or knocking noise caused by exces-sive camshaft endplay

An irregular slapping or thumping at the front of the en-gine caused by a loose timing belt. A tight belt makes awhirring, whining, hum that rises and falls in pitch withRPM

A single, clear clack whenever a particular valve opens canbe a collapsed lifter or a broken valve spring.

A loud, cycling, valve rattle that you can hear over the nor-mal valve noise can indicate either worn valve guides orrocker arm pivots

Low pressure or restricted oil flow will produce an excessivelyloud, rhythmic clatter

Bottom-End NoisesHealthy engines produce an evenly pitched, rapid, whirringsound and nothing else. Knocking or thumping noises are



signs that something is wrong. In general, bottom-end noisecan be caused and indicated by:

An irregular knock at idle that can be made louder orfainter by playing with the clutch pedal indicates toomuch crankshaft endplay

A sharp clattering knock that may be continuous at idle oronly appear when the throttle closes suddenly can indicatea bad connecting rod bearing. The noise will diminish ifthe spark plug for the offending cylinder is grounded

A hollow metallic clatter that is loudest when the engineis cold may be piston slap caused by too much piston-to-cylinder wall clearance. Grounding the spark plug of theaffected cylinder will often make piston slap louder be-cause it eliminates the cushioning of the extra gas pressurepushing on the piston

A sharp knocking that stands out most at idle can indicatea wrist pin that is loose in its bore. Grounding the sparkplug of the affected cylinder makes the knock audible attop dead center as well as bottom dead center. Retardingthe spark decreases wrist pin noise

A rapid, steady dull pounding that increases with load istypical of worn main bearings

Spark KnockSpark knock, which is caused by uncontrolled combustion,sounds like a metallic pinging noise. Spark knock may be heardunder a heavy load or on acceleration.

Detonation occurs when combustion of the air/fuel mix-ture in the cylinder starts off correctly in response to ignitionby the spark plug, but one or more pockets of the air/fuel mix-ture explode outside the envelope of the normal combustion.The collision of the two flames causes a pinging noise. This canbe caused by:

Fuel with too low an octane rating Ignition timing that is too far advanced High engine operating temperature Excessive carbon build-up in the combustion chamber

Preignition occurs when the air/fuel mixture prematurely ig-nites before the spark plug fires. Then the spark plug ignites theremaining mixture at the normal time. When the two portionsof burning mixture meet each other, there is a sudden abnor-mal rise in cylinder pressure causing engine vibration and apinging noise. This can be caused by:

Hot spots in the combustion chamber Incorrect heat range spark plug Carbon deposits in the combustion chamber

Unusual Exhaust Color and OdorAlthough a healthy catalytic converter can do a good job ofcleaning up the exhaust, you can tell something about theinternal engine condition by checking for unusual smoke orsmells:

Black exhaust smoke. This is caused by a rich air/fuel mix-ture and is often accompanied by the rotten egg smell ofan overworked catalytic converter

Blue exhaust smoke indicates excessive oil burning, whichgives off a pungent odor

Cloudy white exhaust is often the result of engine coolantleaking into the combustion chamber. Burning coolantalso produces a distinctive chemical odor. Check the tem-perature gauge for overheating

Keep in mind that oil vapor odors are not always the result ofan internal engine problem. A clogged or malfunctioning pos-itive crankcase ventilation (PCV) system can not only producea burning oil smell, but can also cause excessive crankcasevapor and increase oil consumption. Always check all externalsources before you condemn the engine.

Internal Engine DiagnosisSpecific internal mechanical problems on a running enginecan be located by performing several basic tests. To eliminatethe possibility of internal engine problems, perform the fol-lowing tests:

Intake manifold vacuum Cylinder compression Cylinder leakage Cylinder power balance

A brief description of standard test procedures and interpret-ing results will be presented here.

Intake Manifold Vacuum TestsManifold vacuum tests are performed by connecting a vacuumgauge to the intake manifold downstream of the throttle plates.The gauge records the difference between atmospheric pres-sure and manifold pressure. Vacuum gauge readings can pin-point manifold and vacuum line leaks, valve and valve guideproblems, incorrect ignition and valve timing, exhaust restric-tions, and poor combustion chamber sealing.

A vacuum gauge is usually calibrated in inches of mercury(in-Hg) or kilopascals (kPa). Normal vacuum at idle is from 15 to21 in-Hg (50 to 70 kPa) for most engines. Gauge readings shouldbe steady and decrease as the throttle opens. Vacuum decreases aselevation increases, and gauge readings must be corrected ac-cordingly. Manufacturers provide specifications for testing at sealevel. To correct for altitude, subtract one in-Hg (3.377 kPa) forevery 1,000 feet (305 meters) above sea level.

Some engines, especially if turbocharged or supercharged,require a measure of manifold boost pressure test. Boost pres-sure, also known as positive pressure, specifications are providedby the manufacturer. Gauges for reading manifold absolutepressure (MAP) may be calibrated differently than vacuumgauges. Absolute pressure uses a reference point of zero pressure,or total vacuum, regardless of atmospheric pressure.

Refer to Book A1 Engine Repair in this series for moredetailed information on manifold vacuum test procedures andresults.

Cylinder Power Balance TestThe Powertrain Control Module (PCM) in most late-modelvehicles incorporates the ability to conduct a power or cylin-der balance test utilizing a diagnostic scan tool. The scan toolcommands the PCM to run the test either automatically ormanually at the operators discretion. Each cylinder is disabledby shutting off the fuel and in some cases the spark to the cylin-der being tested. The average RPM drop is displayed on the


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scan tool screen and can be related directly to the contributionof that cylinder.

Most older engine analyzers have the capability of per-forming a power balance test, figure 1-2. The balance testshows if an individual cylinder or a group of cylinders is notproducing its share of power. During the test, the spark plug isshorted so there are no power strokes from the cylinder beingtested. Results are measured in terms of engine RPM drop,manifold vacuum drop, or a combination of these factors.

If the changes in engine RPM and manifold vacuum areabout the same for each cylinder, the engine is in good me-chanical condition. If the changes for one or more cylinders arenoticeably different, the engine has a problem. The fault may bemechanical, or it may be in the ignition or fuel systems.

A power balance test is not conclusive; further tests areneeded to pinpoint the problem. The procedure can be a timesaver because it is performed on a running engine. An enginethat passes a cylinder balance test will have fairly even com-pression, so there is usually no need to perform compressionand cylinder leakage tests.

Cylinder Compression TestsThe compression test reveals how well each cylinder is sealedby the piston rings, valves, cylinder head gasket, and the sparkplug. Compression pressure is measured in pounds per squareinch (psi), kilopascals (kPa), or bars. The following quantitiesare equal to each other: 14.5 psi, 100 kPa, and 1 bar. A com-pression gauge measures the amount of air pressure that acylinder is capable of producing.

Compression test specifications and procedures for anengine are normally provided in the vehicle Service Manual.Follow the steps in the Service Manual to prepare the enginefor a compression test, then install the compression tester,figure 1-3, and run the test.

In general, a compression test is performed with theengine at normal operating temperature, all spark plugs re-moved, the ignition disabled, the battery fully charged, and thethrottle held in wide-open position. Interpret compressiongauge readings as follows:

Compression is normal when the gauge shows a steadyrise to the specified value with each compression stroke

If the compression is low on the first stroke and builds upgradually with each succeeding stroke, but not to specifica-tions, the piston rings or cylinder walls are probably worn

A low compression reading on the first stroke that buildsup only slightly on the following strokes indicates stickingor burned valves

Two adjacent cylinders with equally low compression in-dicates a head gasket leak between them

A higher than normal compression reading usually meansexcessive carbon deposits have formed on the piston top orin the combustion chamber. Fluid, such as oil, coolant, orfuel in a cylinder, also produces high compression pressure

Cylinder Leakage TestA cylinder leakage tester, or leak-down tester, gives more de-tailed results than a compression test. Used as a follow-up tocompression testing, a leakage test can reveal:

The exact location of a compression leak How serious the leak is in terms of a percentage of total

cylinder compression

The tester forces air into the combustion chamber through thespark plug hole. A gauge installed in the air line indicates howmuch pressure leaks out of the combustion chamber. Thegauge scale is graduated from 0 to 100 percent.

Calibrate the leakage tester according to the equipment in-structions before testing. To test a cylinder, the piston must beat TDC of the compression stroke so that both valves are closed.Install the test adapter in the spark plug opening, connect theair hose, and pressurize the cylinder. Note the percentage read-ing on the scale and interpret as follows:

0-10 percent Good 10-20 percent Fair 20-30 percent Poor30-100 percent Failed!

For cylinders with more than 20 percent leakage, pinpoint thecause of the leaks as follows:

Air escaping through the air intake indicates a leaking in-take valve

Fig. 1-3. Compression tester gauge installed in the spark plug hole.

Fig. 1-2. Typical engine analyzer power balance panel.



Air escaping through the exhaust indicates a leaking ex-haust valve

Air escaping through the crankcase and PCV system indi-cates worn or damaged piston rings, worn cylinder walls,or a worn or cracked piston

Air bubbles in the coolant indicate a leaking head gasketor a crack in the engine block or cylinder head casting

High readings on two adjacent cylinders indicate headgasket leakage or a casting crack between cylinders

Ignition System DiagnosisThe automotive ignition system consists of a low-voltage pri-mary circuit and a high-voltage secondary circuit. Voltagevaries within these circuits during operation. An oscilloscopedisplays voltage changes during a period of time, and is anideal instrument for testing ignition system operation.

Traditional automotive oscilloscopes are installed in mul-tifunction engine analyzer units that also contain voltmeters,ammeters, ohmmeters, tach-dwell meters, vacuum and pres-sure gauges, timing lights, and exhaust analyzers. Small hand-held oscilloscopes that can also monitor the low-voltage signalsof the engine management system are gaining in popularity.

All oscilloscopes work on the same principle: A voltagetrace of the system being tested is displayed on a viewingscreen. Voltage traces are displayed as a graph of voltage overtime. The vertical scale on the screen represents voltage and thehorizontal scale indicates time. The voltage range of the scopeis generally adjustable. Primary circuits are measured in voltsand secondary circuits in kilovolts (kV), or thousands of volts.Time is measured either as a percentage of one complete en-gine cycle or in milliseconds (mS), thousandths of a second.

An ignition system voltage trace, both primary and sec-ondary, is divided into three sections, firing, intermediate, anddwell, figure 1-4. Deviations from a normal pattern indicate aproblem. In addition, most scopes will display ignition tracesin three different patterns. Each pattern is best used to isolateand identify particular kinds of malfunctions. The three basicpatterns are:

Superimposed pattern Parade pattern Stacked or raster pattern

In a superimposed pattern, voltage traces for all cylinders are dis-played one on top of another to form a single pattern, figure 1-5.This display provides a quick overall view of ignition systemoperation and can also reveal certain major problems.

The parade pattern displays voltage traces for all cylindersone after another across the screen from left to right in firingorder sequence, figure 1-6. This allows easy comparison ofvoltage levels between cylinders. A parade display is useful fordiagnosing problems in the secondary circuit.

A raster pattern shows the voltage traces for all cylidersstacked one above another in firing order sequence, figure 1-7.This display allows you to compare the time periods of thethree sections of a voltage trace.

Primary Ignition PatternsPrimary scope patterns are displayed as a low-voltage tracemoving from left to right across the screen. Electronic ignition

Fig. 1-4. Primary and secondary ignition oscilloscope patterns.

FIRINGSECTION

INTERMEDIATESECTION

DWELLSECTION

ALL CYLINDERS

90

60

80

50

70 60

40

50

30

40 30

20

20

10

4 CYL6 CYL

8 CYL

0

0045 40 35 30 25 20 15 10

Fig. 1-5. All cylinder traces are displayed one on top of anotherin a superimposed pattern.

Fig. 1-6. Cylinder traces are displayed one after another in aparade pattern.

patterns vary by system, so it is important to know what isnormal for the system being tested. Scope manufacturers gen-erally provide sample patterns for comparison.


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Firing SectionThe firing section of the pattern corresponds to the amountof time the spark plug is firing. The voltage trace recordsinduced voltage surges in the primary circuit as secondaryvoltage is being dissipated from the coil. A typical patternbegins with a vertical rise as spark is established, which isfollowed by a series of diminishing oscillations until the sparkis extinguished, figure 1-8.

With some electronic ignition systems, there are no oscil-lations. Firing is displayed as a vertical spike followed by a rela-tively flat line until the spark ends. In parade display, the heightof the oscillations should not vary between cylinders.

Intermediate SectionThe intermediate section begins when the spark stops and con-tinues until the primary circuit is switched on by an electronicsignal, figure 1-9. Some ignition systems do not have an inter-mediate section, and the primary circuit is switched on themoment the spark is extinguished.

The voltage trace is created by the dissipation of energyremaining in the coil after firing. A series of diminishing oscil-lations, similar to the firing section but considerably smaller, isnormal.

Dwell SectionThe dwell section is the time the primary circuit is completeand a low-voltage current flow is building up the magneticfield of the coil. The trace should drop sharply to level off in arelatively flat horizontal line. Dwell ends with the abrupt up-ward stroke of the first firing oscillation.

Use the raster pattern to compare the dwell period foreach cylinder. Dwell sections should not vary by more thanfour to six degrees between cylinders. Variations can be causedby a worn distributor, timing chain, or faulty crankshaft posi-tion sensor (CKP).

Secondary Ignition PatternsSecondary voltage traces also move left to right across thescreen in firing, intermediate, and dwell sequence. Oscillationsare displayed on a high-voltage scale. Normal firing voltagewith an electronic ignition system can exceed 40 kV.

Firing SectionThe firing section of the secondary pattern begins with astraight vertical line that indicates the amount of voltage re-quired to create an arc across the spark plug air gap. This iscalled the firing line or voltage spike. When the arc is estab-lished, less voltage is required to maintain it and the tracedrops to about one-quarter the height of the voltage spike,then continues horizontally as the sparkline. The sparkline,which represents continued current across the spark plug gap,may have a series of very small oscillations.

Intermediate SectionThe secondary intermediate trace indicates excess coil voltagebeing dissipated and is similar to that of the primary ignitionpattern. Look for a short vertical rise from the sparkline fol-lowed by diminishing oscillations. Oscillations should be ofrelatively even width and taper down gradually to a near hor-izontal line. The intermediate section ends as the primarycircuit is switched on.

Dwell SectionThe dwell section begins as the primary circuit is switched onand continues until the firing section begins. A typical trace

FIRING ORDER

4

2

6

3

5

1

25

20

15

10

Fig. 1-7. The raster pattern stacks the cylinder traces on top ofone another.

SPARK BEGINS

FIRING SECTION

SPARK ENDS

FIRING LINEDIMINISHINGOSCILLATIONS

Fig. 1-8. A normal primary circuit firing trace.

PRIMARY CIRCUITSWITCHES ON

INTERMEDIATESECTION

SPARK ENDS

Fig. 1-9. The intermediate section begins as the spark extinguishesand continues until the primary circuit is switched on.



pattern shows the switching as a sharp downward spike fol-lowed by a series of small diminishing oscillations that level offto a nearly flat line. The length of the dwell section and thetrace pattern may be engine speed dependent, and varies fordifferent systems, figure 1-10. Some switching signals producea series of oscillations; others do not. All begin with a sharpvertical drop and continue as a nearly flat horizontal line.

Fuel System DiagnosisFuel system malfunctions can cause an assortment of drive-ability problems, such as engine surging, stalling and misfiring,hard or no starting, and poor fuel mileage. A restriction some-where in the fuel or air supply is often the cause. Pressure testingis the most effective way to locate fuel supply problems. Testprocedures are covered in Chapter Three of this book.

The results of engine diagnostic tests, such as manifoldvacuum, cylinder power balance, oscilloscope analysis, exhaustgas analysis, and onboard diagnostics, may indicate fuel systemproblems.

When checking manifold vacuum, look for an oscillatingneedle with a reading slightly below normal at idle. This indi-cates an incorrect fuel mixture. A defective port fuel injectorcan cause a cylinder with good compression to show poorpower balance test results. Onboard diagnostic tests can revealfaults in the electronic circuits. For oscilloscope patterns thatindicate fuel problems, refer to Ignition System Diagnosis, dis-cussed previously.

Electrical System DiagnosisHard starting, no start, and slow cranking speed can indicate anelectrical problem. Check the battery, starting system, andcharging system. Specific testing procedures are covered inChapter Six of this book. Most minor electrical and electronicsystem malfunctions can be detected by self-diagnostic and scantool testing. Individual components are tested with a digitalmultimeter (DMM), or oscilloscope. Component testing is de-tailed in the subsequent chapters of this book. Accessing and in-terpreting stored computer codes will be discussed there as well.

Onboard Diagnostic SystemsThe computers used in late-model engine control systems areprogrammed to check their own operation, as well as the

operation of each sensor, actuator, and circuit, figure 1-11.Whenever the computer recognizes a signal that is outside itslimits, it records a diagnostic trouble code (DTC) in its memory.

Generally, the computer is capable of recognizing thefollowing:

A particular signal, such as engine speed, is not beingfurnished

A signal that is out of limits for too long, such as a too-richor too-lean oxygen sensor (HO2S) signal

An improbable signal, such as input from a barometricpressure sensor that indicates the vehicle is being driven atan altitude of 25,000 feet

Some systems have the ability to test sensor or actuator circuitcontinuity by sending out a test signal and monitoring thevoltage of the return signal.

When an out-of-range signal is detected, the computerrecords it as either a continuous or intermittent fault. A contin-uous, or hard, failure indicates that the malfunction occurredand is still present. These generally result from the total failureof a component or subsystem. An intermittent, or soft, failureindicates that the malfunction took place momentarily, then dis-appeared. This type of code usually means that a component orsubsystem is functioning erratically, and is often caused by aloose, dirty, or weak connection. Most systems will store anintermittent DTC in the long-term memory for 50 to 60 engine-start cycles.

Retrieving CodesMost vehicles have a diagnostic connector, or data link con-nector (DLC), for accessing the computer memory. On oldermodel vehicles, the multi-plug connector can be either underthe hood or in the passenger compartment. The DLC is alwaysin the passenger compartment on late-model, Onboard Diag-nostic II (OBD-II)compliant vehicles. The DLC permits con-nection of a test meter or jumper wire to trigger the diagnosticmode. A DTC is displayed generally in one of four basic ways:

Numerical display on a scan tool Pulsating voltmeter needle Pulsating instrument panel lamp On a digital instrument cluster display panel

The manner in which the program is activated and thesequence in which codes are displayed vary between manufac-turers. The preferred method of DTC retrieval is with a scantool, figure 1-12. However, not all systems transmit codes to ascan tool, and codes must be read some other way. Each man-ufacturer publishes a list of trouble codes used with theirsystems and specific instructions for retrieving codes andclearing the computer memory.

Interpreting Diagnostic Trouble CodesWhen properly used, a DTC helps to organize an efficientapproach to isolating the source of a problem. Although trou-ble codes are a valuable diagnostic aid, they will not reveal theprecise cause of a problem. However, a DTC does indicatethe particular circuit where a malfunction took place. Anaccurate troubleshooting chart from the manufacturer isrequired to determine what may have set the code.

Fig. 1-10. Dwell time increases with engine speed on someelectronic control systems.


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Fig. 1-11. The onboard diagnostic system, which monitors sensor and actuator signals, records a DTC when a circuit abnormality occurs.

Fig. 1-12. Retrieving codes with a scan tool.

Stored codes are often the result of poor circuit connec-tions rather than a component failure. Engine sensor systemsoperate on low voltage, usually 5.0 volts, and relatively minorchanges in resistance will interfere with the signal. Stored codesmay be the result of a mechanical problem, and additional en-gine tests are required to isolate the source. Always check thecircuitry and connections before replacing any electronic parts.

Simply disconnecting and reconnecting a multi-plug willoften clean the contacts, restore continuity, and eliminate thecode. When multiple codes are present, look for a weak

connection at a common grounding point. An open circuitresults in either a signal not being generated or received. Low-voltage signals can indicate a shorted circuit.

Individual circuits, sensors, and actuators can be checked byconnecting a breakout box (BOB) to the computer, figure 1-13.The breakout box allows you to monitor the individual circuitsignals with a digital multimeter (DMM) or oscilloscope. Pro-cedures for testing components are discussed in the appropri-ate chapters of this book.

Exhaust Gas AnalyzersTo properly diagnose fuel system concerns an exhaust gasanalyzer should be used, figure 1-14. The analyzers are avail-able in many styles and designs. Current models are designedto sample and analyze either four or five gases present in theexhaust from the vehicle. The newest models are designedfor five-gas detection and normally provide digital and/orprinted results of each test. Either piece of equipment is gen-erally suitable for diagnosing basic fuel system abnormalitiesand driveability problems. The five-gas units are required inmany jurisdictions to permit the technician to verify emissionscompliance of a vehicle.

Five-Gas AnalyzersFive-gas analyzers measure the parts per million (ppm) ofhydrocarbons (HC), the percentage of carbon monoxide (CO),



the percentage of oxygen (O2), the percentage of carbon dioxide(CO2), and the percentage of oxides of nitrogen (NOx). Mostproperly tuned computer-controlled vehicles will produce about50 ppm of HC, less than 0.5 percent CO, 1.0 to 2.0 percent O2,and 13.8 to 15.0 percent CO2.

Four-Gas AnalyzersFour-gas analyzers measure HC, CO, CO2, and O2. They donot provide data as to the levels of NOx in the exhaust.

Diagnosing Exhaust GassesTo assist with the discussion that follows, refer to the diag-nostic chart for problems that may cause abnormal readings,figure 1-15.

For an accurate analysis of fuel combustion on catalyticconverter-equipped vehicles, prevent the air injection systemfrom supplying oxygen into the exhaust stream. This de-creases the amount of O2 at the tailpipe, and the efficiency ofthe converter. The air injection system may be disabled byseveral means. On some vehicles, disconnecting the air injec-tion pump or plugging the pulse air injection system is effec-tive. For others, the probe of the analyzer can be connectedto a port installed upstream of the catalytic converter or tothe exhaust opening for the EGR valve. Next, make sure thatthe engine is at operating temperature, in closed loop, andthe HO2S is transmitting a variable signal. Sample the ex-haust gases both at idle and at 2,500 RPM. If a dynamometeris used, test under simulated highway load conditions as de-scribed by the manufacturer.

Abnormal HC and CO ReadingsHigh HC levels indicate unburned fuel in the exhaust causedby incomplete combustion. The source of high HC emissionscan often be traced to the ignition system, but mechanical or fuelsystem problems also can increase HC emissions, figure 1-16.High levels of HC emissions result from:

Advanced ignition timing Ignition misfire from defective spark plug wires or fouled

spark plugs An excessively rich or lean air-fuel mixture Leaking vacuum hoses, vacuum controls, or seals Low engine compression Defective valves, valve guides, valve springs, lifters,

camshaft, or incorrect valve lash Defective rings, pistons, or cylinder walls Clogged fuel injectors causing a lean misfire

The amount of CO in the exhaust stream is directly propor-tional to the amount of O2 contributing to the combustionprocess. Richer air-fuel mixtures, with lower oxygen content,produce higher CO levels; leaner air-fuel mixtures, with high-er oxygen content, produce lower CO levels. High CO emis-sions may result from one or more of the following abnormalconditions:

Clogged or dirty intake air passages Plugged air filter element Throttle body coking Rich fuel mixture Incorrect idle speed Excessive fuel pressure Leaking fuel injectors

Both HC and CO levels reading high at the same time may becaused by the following conditions:

Defective positive crankcase ventilation system Defective catalytic converter Defective manifold heat control valve Defective air pump Defective thermostatic air cleaner

Abnormal CO2 and O2 ReadingsSince the catalytic converter reduces HC and CO, these emis-sions are unreliable for determining the air-fuel ratio. However,

Fig. 1-13. Typical breakout box.

Fig. 1-14. Typical exhaust gas analyzer.


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CO2 and O2 readings can be useful, provided that the airinjection system has been disabled.

When air and fuel entering the engine burns with the leastamount of wasted energy, at the stoichiometric air-fuel ratio,the engine emits the highest amount of CO2. Look for read-ings between 13.8 and 15 percent. As the air-fuel ratio of themixture leans or enriches, the CO2 level drops. To determinewhether a low CO2 level indicates a lean or rich condition,examine the O2 reading. Levels of O2 below approximately

1.0 percent indicate a rich-running engine; above 2.0 percentindicate a lean-running engine.

To perform adequately and operate efficiently, an enginemust be in sound mechanical condition. Therefore, it is im-portant to determine the overall mechanical condition of theengine before attempting to isolate or repair the cause of a drive-ability or performance problem.

Perform a compression or cylinder leakage test to deter-mine the internal sealing capabilities of the engine. When test

EMISSION IDLE OFF IDLE

CRUISE 18002000

VAIR-FUEL RATIO

POSSIBLE CAUSES RELATED SYMPTOMS

CO 3% 3% 3%

HC 250 ppm

280 ppm

300 ppm

CO2 79% 79% 79% 1

O2 .2% .2% .2%

Rich AFR Below 10:1

Vacuum leak to map sensor Fuel injectors leaking Bad Power Valve (carburetor) Excessive fuel rail pressure Vacuum diaphragm bad

Black smoke or sulfur odor Engine in open loop Surge/hesitation Engine not preconditioned

CO 1.5% 1.5% 1.5%

HC 150 ppm

150 ppm

200 ppm

CO2 79% 79% 1113% 2

O2 .2% CO .2%

Rich AFR at low speed 1012:1

Engine oil diluted w/ fuel Carburetor idle speed Cold engine Idle mixture too rich Choke stuck shut PCV valve defective Fuel injectors leaking

Poor fuel economy Sooty spark/black smoke Rough idle/surge hesitation Vapor canister purge valve bad Vapor canister saturated

CO 0.5% 0.5% 1.0%

HC 200 ppm

200 ppm

250 ppm

CO2 79% 79% 79% 3

O2 45% 45% 45%

Lean AFR Over 16:1

Check ignition primary/secondary Vacuum leak Carburetor mixture lean Poor cylinder sealing Fuel injectors restricted Improper timing Exhaust valve leak

Rough idle Misfire high speed Detonation cruise (2000 rpm) Idle hunting (computer) Overheating

CO 2.5% 1.0% 0.8%

HC 100 ppm

80 ppm 50 ppm

CO2 79% 79% 79% 4

O2 23% 23% 23%

Lean AFR at High Speed Over 16:1

Air cleaner heater door closed Internal carburetor problem (float tuck, wrong jet, metering rod stuck) Fuel injectors restricted Fuel pump pressure low

Rough idle Misfire Surging Hesitation

CO 0.3% 0.3% 0.3%

HC 100 ppm

80 ppm 50 ppm

CO2 1012% 1012% 1012% 5

O2 2.5% 2.5% 2.5%

AFR 1315:1

Engine not preconditioned Air management system not disabled Converter not warmed

None No driveability symptoms

Fig. 1-15. Four-gas exhaust emissions failure chart.



results are marginal and indicate valve seating problems, per-formance can often be restored by adjusting valve lash orservicing hydraulic valve lifters. If test results are below speci-fications, internal engine repairs are required to restore per-formance. This chapter focuses on engine repairs that can beperformed without disassembling the engine or removingmajor components.

VALVE LASH ADJUSTMENTIdeally, an engine should operate with near zero valve lash,or clearance. Under these conditions, valve movement fol-lows the profile of the camshaft lobe exactly to provide

efficient operation. Over the life of an engine, valve clearancetends to change as a result of wear on the valve face, valveseat, pushrod, and rocker arm. For many years engines weredesigned with provisions to make periodic adjustments tocorrect for this wear. Many late-model engines have noscheduled need for and therefore no provision for making avalve clearance adjustment. These engines require precisemachining during overhaul to ensure that the proper clear-ances are met. If valve clearance problems surface diagnosiswill reveal a failed component. Follow the Service Manualprocedures for repair or replacement of the component orcomponents involved.

HC CO CO2 O2 NOx

Ignition Misfire

Compression Loss

Rich Mixture

Lean Mixture

Minimal Timing Retard

Excessive Timing Retard

Advanced Timing

EGR Operating

EGR Leaking

AIR Operating

Converter Operational

Exhaust Leak

Worn Engine

Worn CamshaftLobes

LargeIncrease

Some Decrease

SomeDecrease

Some to Large Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Decrease

Some Increase

Some Decrease

Some Decrease

Some to Large Increase

Some to Large Increase

LargeIncrease

Some Decrease

Some Increase

LargeDecrease

Some Increase

LargeIncrease

PossibleIncrease

NoChange

NoChange

PossibleDecrease

Some Increase

Some Increase

NoChange

NoChange

Some to Large Decrease

LargeDecrease

LargeDecrease

Some Decrease

LargeIncrease

NoChange

NoChange

Small Decrease Possible

NoChange

NoChange

NoChange

LargeDecrease

Some Increase

NoChange

NoChange

PossibleIncrease

NoChange

LargeDecrease

LargeDecrease

LargeDecrease

LargeIncrease

PossibleIncrease

Some Increase

LargeDecrease

Some Increase

NoChange

Some Increase

Some Increase

LargeDecrease

PossibleDecrease

Some Decrease

PossibleDecrease

Condition

Fig. 1-16. Effect of engine condition on the formation of exhaust gasses.


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Valve Lifter DesignsWith hydraulic lifters, once engine oil pressure is established,the lifters automatically take up all slack in the valve train tomaintain zero clearance, figure 1-17. Hydraulic lifters alsocompensate for metal expansion as the engine warms up. Hy-draulic valve lifters do not require routine adjustment.

Mechanical lifters must be set with a precise amount ofclearance so that the valves operate with close to zero lash oncethe engine is at normal operating temperature. Mechanicallifters must be adjusted periodically to compensate for wear inthe valve train.

Maintaining the correct clearance is important. Too muchclearance prevents the camshaft from opening the valves fully.This shortens effective camshaft duration, causing valves toopen late and close early, which reduces engine efficiency andperformance. Continued operation stresses valve train partsand can lead to premature failure.

Insufficient clearance causes the valves to open too far. Ef-fective duration is increased so the valves open early and closelate. Once the engine warms to operating temperature, thevalves might not be able to close completely.

Adjustment MethodsTypical valve clearance specifications range from 0.004 to 0.025inch (0.10 to 0.64 mm) for intake valves and 0.004 to 0.030 inch(0.10 to 0.76 mm) for exhaust valves. Service Manuals may listvalve clearances either as hot or cold specifications, or both.If the valves are to be set cold, check the coolant temperature.It should be about the same as the air temperature, and thevalve cover should feel cool to the touch. To use a hot specifica-tion, the engine should be warmed to its normal operating tem-perature. Common adjustment mechanisms include:

An adjustment locknut holding the rocker arm to therocker stud

Replaceable adjustment shims located between thecamshaft lobes and cam followers

Selective length pushrods

Adjusting Clearance on Overhead Valve EnginesAll late-model domestic overhead valve (OHV) engines usehydraulic lifters. Adjustments are required only after high-mileage operation has worn valve train parts beyond the adjust-ment range of the lifters, or when the rocker arms, pushrods, orlifters were removed for service. Mechanical valve lifters are stillused on some import and high-performance engines.

To access the lash adjusters, remove the valve covers.When hot clearance specifications are provided, valves canoften be adjusted while the engine is running. Cold clearancesare set with the engine off and cooled down. Both proceduresare presented here.

Adjusting Clearances with the Engine RunningWith many OHV engines, valve lash can easily and accu-rately be adjusted with the engine running at its normaloperating temperature. Remove the valve covers and installa set of oil deflectors on the rocker arms to prevent oil fromsplashing.

Obtain the proper hot valve clearance specifications andhave the necessary feeler gauges and wrenches readily available.Work from one end of the engine to the other and set all of theintake valve clearances first. Then, repeat the sequence to ad-just all of the exhaust valves.

Hydraulic LiftersStud-mounted adjustable rocker arms used with hydrauliclifters can also be adjusted with the engine running.

Follow this procedure:

1. Starting with any valve, back off the rocker arm locknutuntil the valve starts to clatter. At this point, the valve hastoo much clearance.

2. Slowly tighten the nut until the clatter just stops. Thisremoves all lash, but does not compress the plunger intothe lifter body so there is no reserve travel left to com-pensate for wear.

3. Slowly tighten the locknut in 90 degree increments, wait-ing about 10 seconds between steps to give the lifter timeto bleed down. The total amount the locknut is tightenedvaries between engines. Check the Service Manual forspecifications.

Adjusting Clearances with the Engine OffWith the engine not running, the cylinder to be adjusted mustbe brought up to top dead center (TDC) so that both valves are closed. For engines with mechanical lifters, turn the ad-justment screw until there is a slight drag on the feeler gaugeblade. Some engines use interference-fit adjustment screws ornuts that retain their position once they are tightened. Othersuse a locknut to hold an adjustment screw in place once thecorrect clearance is established. On these engines, alwaysrecheck clearance after tightening the locknut.

Two adjustment methodsselective length pushrodsand adjustable rocker armsare used on engines with hydraulic lifters.Fig. 1-17. Typical hydraulic lifter.



Mechanical LiftersThe following general procedure can be used to adjust valveclearance with mechanical lifters on a running engine:

1. Make sure the engine is running at its slowest idle speedand is at normal operating temperature.

2. Insert a feeler gauge of the correct thickness between therocker arm and valve stem. The feeler gauge should passthrough the gap with a slow, steady drag:

If force is required to insert the feeler gauge, or if theengine starts missing when the gauge is inserted, theclearance is too tight

If the gauge slips through too easily, or if there is achoppy, jerking feel as the gauge passes through, theclearance is too loose

3. Turn the adjusting screw in or out as required.4. Recheck the clearance after adjustment. If a separate

locknut is used, check the clearance once again aftertightening the locknut.

Selective Length PushrodsA few older engines with non-adjustable valve gears use zero-lash hydraulic lifters. However, to allow for valve train wear, theplunger of the lifter must be centered inside the body. This isaccomplished by installing shorter or longer pushrods. Tocheck and adjust clearance:

1. Position the cylinder at TDC on its firing stroke.2. Tighten the rocker arm locknut to the torque value spec-

ified by the manufacturer.3. Depress the pushrod end of the rocker arm with a tappet

bleed down wrench, a large screwdriver, or other suitabletool to bottom the plunger in the lifter.

4. Hold the end of the rocker arm down, and measure theclearance between the valve stem tip and the rocker.

5. Compare this value to the specification range for that en-gine. If the clearance is too great, install a longer pushrod.If it is too little, install a shorter pushrod.

Pushrods for most engines are available in three sizes: stan-dard, 0.060 inch (1.5 mm) oversize, and 0.060 inch (1.5 mm)undersize. In general, pushrods need to be changed only afterthe head and block mating surfaces have been resurfaced, orthe valve seats have been replaced or excessively machined.

Setting Adjustable Rocker ArmsTo set adjustable rocker arms with the engine not running,follow this procedure:

1. Position a cylinder at TDC on its power stroke so bothvalves are closed.

2. Slowly tighten the rocker arm locknut to remove all theslack from the valve train without compressing thehydraulic lifter. The pushrod will no longer rotate freelyand the rocker can no longer wiggle from side to side,figure 1-18.

3. Slowly tighten the rocker arm locknut an additionalthree-quarters to one-and-one-half turns to position theplunger in the center of its travel inside the lifter. Howmuch additional tightening is required varies by engine.Check the Service Manual for exact specifications.

Adjusting Clearance on Overhead Camshaft EnginesOnce the valve cover is removed on an overhead cam (OHC)engine, the camshaft contacting the lifter is visible. Rotate theengine by hand while watching the camshaft lobes to bringthe cylinder to be adjusted into position. Position thecamshaft so that the base circle of a cam lobe is directly in linewith its follower or rocker arm pad. Then, that valve is closedand a feeler gauge blade can be inserted to check the clear-ance. If the engine uses a screw-type adjuster, simply loosenthe locknut and reposition the screw until there is a slightdrag on the feeler gauge, figure 1-19. Tighten the locknut,recheck clearance, and move on to the next valve. Continueuntil all the valves are set.

Setting Valve Lash with Replaceable ShimsThe replaceable adjustment shims on most engines are locatedbetween the camshaft lobe and cam follower. A special toolis used to depress the follower so the shim can be removed,

Fig. 1-18. Typical adjustable rocker arm service.

ADJUSTINGSCREW

LOCKNUT

VALVE SPRING

EXHAUSTVALVE

ROCKERARM

ROCKERSHAFT

CAMSHAFT

INTAKEVALVE

Fig. 1-19. Overhead cam engine with rocker arms and screw-type adjusters.


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figure 1-20. To adjust the valve clearance, follow this generalprocedure:

1. Position the cylinder to be checked at TDC.2. Measure the clearance with a feeler gauge.3. Compress the follower and hold it down using the spe-

cial tool.4. Pry the shim loose with a small screwdriver, or other suit-

able tool, and remove it with a magnet or pliers.5. Measure the thickness of the shim with an outside

micrometer.6. Calculate the thickness of the shim to be installed:

Subtract the midpoint of the specified clearance rangefrom the measured clearance

Add the result to the thickness of the shim that was re-moved from the engine

The result equals the thickness of the new shim to beinstalled

7. Install the new shim in the recess in the top of the lifterand firmly seat it into place.

8. Release the follower and recheck the valve lash clearance.

Some engines use a smaller shim that fits directly on top of thevalve stem underneath the cam follower. To replace this type ofshim, the camshaft and the follower must be removed.

CAMSHAFT AND VALVE TIMINGCamshaft timing can be verified by removing the timing coverand inspecting the timing marks, figure 1-21, or by using adegree wheel and dial indicator. Incorrect valve timing gener-ally results from component wear. Disassemble the camshaftdrive, inspect all components, and replace all worn or damagedparts with new ones. Make sure both the crankshaft andcamshaft remain in the TDC position and all timing marks arealigned during assembly. Once the camshaft drive is in place, fol-low the Service Manual procedures for rotating the engine and

verifying the alignment of the timing marks. Once you haveverified that all timing marks are again in alignment and thatthe chain or belt is properly tensioned, install the timing cover.

Under normal conditions, the initial valve timing of theengine does not change. However, high-mileage operation cancause both timing chains and belts to stretch or tensioners toweaken to the point where valve timing is altered, figure 1-22.Excess slack in the drive assembly causes the camshaft sprocketto lag behind the crankshaft sprocket as the engine runs. Theresult is retarded valve timing that can cause a lack of power

SPROCKETTIMING MARK

CAMSHAFTSPROCKET

CRANKSHAFTSPROCKET

ENGINE CASETIMING MARK

SPROCKETTIMING MARK

CYLINDER HEADTIMING MARK

Fig. 1-21. Typical timing belt arrangement for OHC engine.

SPECIALTOOL

ADJUSTINGSHIM

MAGNET

Fig. 1-20. Depress the follower with the special tool toremove/install the adjuster shim.

CRANKSHAFT

Fig. 1-22. Overhead cam V-type engine timing chain arrangement.



at higher engine speeds and loads. Symptoms are the same asthose caused by retarded ignition timing or a lack of timingadvance.

Variable Valve Timing

Intake camshaft timing is continuously variable using ahydraulic actuator attached to the end of each intakecamshaft. Engine oil flow to each hydraulic actuator iscontrolled by a camshaft position actuator control sole-noid. Exhaust camshaft timing is fixed.

A single timing chain drives both exhaust camshafts andboth intake camshaft hydraulic actuators. While valveoverlap is variable, valve lift and duration are fixed.

Cam timing is determined by the ECM using the crank-shaft position (CKP) sensor and camshaft position sensor(CMP 1 and CMP 2) signals. At idle, the intake camshaftsare fully retarded and valve overlap is zero degrees. Athigher speeds and loads, the intake camshafts can be ad-vanced up to 40 crankshaft degrees.

Each intake camshaft has a separate camshaft positionsensor, hydraulic actuator, and control solenoid. If little orno oil pressure is received by a hydraulic actuator (typi-cally at engine startup, at idle speed or during a fault con-dition), it is designed to mechanically default to the fullyretarded position (zero valve overlap) and is held in thatposition by a spring loaded locking pin.

COOLING SYSTEM SERVICEAn engine that runs too hot or too cold has poor performance,reduced fuel economy, and increased emission levels. Enginetemperatures that are too low or too high are often the resultof a cooling system problem. However, other problems, suchas incorrect ignition timing, overloading the engine, long pe-riods of idling or slow-speed operation, and other factors, cancause overheating as well.

Check the coolant level and test the concentration usinga hydrometer. Look for signs of oil and combustion conta-mination. Engine oil escaping into the coolant will not mix.The oil will float on top of the coolant. Combustion gaseswill chemically react with coolant to rapidly break it down,turning it a rust-brown color. The presence of combustiongases cannot be visually verified. Check using a chemical testkit or exhaust gas analyzer; see Book A1 Engine Repair ofthis series.

Cooling System InspectionUse a pyrometer to monitor actual engine temperature andeliminate the possibility of a faulty gauge, warning lamp, send-ing unit, or circuitry. Once the problem is verified, inspect thecooling system and make the necessary repairs.

Approach diagnosing an overheating problem by firstdetermining when and at what interval the problem occurs.If the owner adds water, find out how much and how often.Secondly, determine whether the problem can be isolated to aspecific driving condition. Visually inspect all cooling systemhoses and replace any that are worn or damaged. Also, inspectthe water pump drive belt for wear, damage, and correct ten-sion and replace or adjust as needed.

Cooling System TestingTesting of the cooling system generally consists of testing thecoolant and performing system and radiator cap pressure tests.If the system and cap both hold pressure, test the operation ofthe thermostat.

Testing the CoolantCoolant concentration and effectiveness are tested with arefractometer or cooling system hydrometer, figure 1-23. Foraccurate results, the coolant should be hot when tested. Beforetesting, draw a coolant sample into the hydrometer and returnit to the radiator several times to stabilize the internal ther-mometer of the hydrometer.

Test as follows:

1. Hold the hydrometer straight and draw enough coolantto raise the float. The float should not touch the sides ofthe hydrometer.

2. With the hydrometer at eye level, take a reading by not-ing the top of the letter on the float that is touched by thecoolant.

3. Find this letter on the hydrometer scale; read down thecolumn under the letter until you are opposite the ther-mometer reading.

4. The number shown at this point is the degree of protec-tion given by the coolant in the system.

System Pressure TestPressure testing the cooling system is a quick and easy way tofind an external leak. Perform the test on a cold engine using ahand pump with a gauge:

1. Remove the pressure cap and attach the pressure tester tothe filler neck.

2. Pump the tester until the gauge reading matches thespecified system pressure, figure 1-24.

3. Observe the gauge; the reading should remain steady.4. If the gauge shows a pressure loss, pump the tester to

maintain pressure and check for leaks.

Radiator Cap Pressure TestCheck the radiator pressure cap using the system pressuretester and an adapter:

1. Attach the cap to the pressure tester.2. Pump the tester until the gauge reading matches the pres-

sure rating of the cap.

Fig. 1-23. Testing engine coolant with a hydrometer.


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3. Observe the gauge; it should hold steady within one ortwo psi of the rating for at least 10 seconds, then gradu-ally decrease.

4. If the reading does not drop at all, continue applyingpressure until the cap vents. The cap should vent whenpressure exceeds the rating by one to three pounds.Replace the cap if it fails either test.

Thermostat ServiceA thermostat that opens above or below its temperature ratingwill cause driveability problems. If the thermostat is stuckopen, or there is no thermostat installed in the system, theengine may never reach an efficient operating temperature.In many instances, the thermostat is defective and should bereplaced. Thermostat function can be checked on a runningengine. Refer to Book A1 Engine Repair in this series formore detailed information on thermostat testing.

Fan Clutch Operation TestA thermometer and an ignition timing light can be used tocheck the operation of a viscous fan clutch. You must knowthe temperature setting of the drive unit. To test:

1. Attach a thermometer to the engine side of the radiator.Be sure it will clear the fan blades and be visible with theengine running.

2. Connect the timing light and start the engine. Note thethermometer reading on a cold engine.

3. Aim the timing light at the fan blades; they should appearto move slowly.

4. Block the radiator to reduce air flow and raise tempera-ture. Do not allow the engine to overheat.

5. Continue watching the thermometer and keep the tim-ing light on the fan blades.

6. When the thermometer reaches the clutch engagementpoint, fan speed should increase. The blades will appearto move faster in the timing light beam.

7. Unblock the radiator so that the temperature drops. Ifthe system is working properly, fan speed will decreasewhen the temperature is below the engagement point ofthe clutch.

Electric Coolant FanElectric coolant fans are designed to operate only when neces-sary, figure 1-25. Several methods are used to control fan operation:

1. A temperature switch that energizes an electrical relay.This switch is usually mounted in the engine.

2. A temperature switch that closes a set of contacts insidethe switch to either complete the power or ground side ofthe circuit for the fan. This switch can be mounted eitherin the engine or radiator.

3. An air conditioning, or high discharge pressure, switch toenergize an electrical relay to turn on the fan.

4. Computer-controlled relays to energize the fans. Thissystem uses the engine coolant temperature sensor tosense engine temperature.

The coolant fan turns on when engine coolant temperaturereaches about 230F (110C). Some systems may have either atwo-speed fan or two separate fans. These systems control fanuse as needed. The fan is also needed to reduce air condition-ing high-side pressures. If the fans are computer controlled,they turn on when the coolant temperature is too high or whenthe computer does not have a coolant temperature sensorreading.

Any diagnosis of the cooling fan begins with an examina-tion of the system wiring diagram. This diagram provides themost accurate and timely understanding of how a particularsystem should operate.

ELECTRICAL WIRING AND SCHEMATICSIn order to understand and diagnose engine performance it isessential that you have a good understanding of electrical fun-damentals and schematics. Generally, schematics can be foundin the Service Manual, although a few manufacturers placethem in a separate book. In either case ensure that the schemat-ic is for the same year and model of vehicle.

Fig. 1-24. Pressure testing the cooling system.

FAN SHROUD

CROSSFLOWRADIATOR

RADIATORFAN SWITCH

AUTOMATICTRANSMISSIONOIL COOLERFITTINGS

ELECTRICFAN MOTORFAN BLADES

Fig. 1-25. Typical electric cooling fan assembly.



Reading Electrical Schematics

Common Symbols and IconsComponents are shown as symbols or icons rather than actu-al pictures in the schematic. Most electrical schematics willhave a table listing the various symbols or icons used in themanual, figure 1-26.

Schematic OverviewThe schematic does not represent the components and wiringas they physically appear on the vehicle. For example, a 4-footlength of wire is represented no differently in a schematic thanone a few inches long, figure 1-27.

The wiring schematic is the cornerstone of electrical di-agnosis. Schematics break the entire electrical system into in-dividual circuits, and show the electrical current paths whena circuit is operating properly. Wiring which is not part of thecircuit of interest is referenced to another page where the cir-cuit is shown complete. Most schematics use a top (power) tobottom (ground) sequence to present electrical information.

Component Location TablesThe Component Location Table, figure 1-28, shows a list of allthe electrical components within a systems electrical schemat-ics and the following information:

All components Grounds Pass-through grommets Splices

The table consists of four columns labeled as follows:

Name Location

Switch

GroundConnector Splice

Motor Battery

IncompleteComponent

View

CompleteComponent

ViewFig. 1-26. Several common electrical schematic symbols.

Fig. 1-27. Typical automotive electrical schematic.


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Locator View Connector End View

NameThe name cells provide the name of the components that areused on the schematic(s). If a connector is listed, the numbersof cavities also are provided.

LocationThe location cell provides a written location of where thecomponent is in the vehicle with respect to the vehicle. Mostcomponents can be located using the component locationview illustrations.

Locator ViewThis column contains the reference to the appropriate locatorview.

Connector End ViewThis column contains the reference to the appropriate connec-tor end view.

How to Use Connector End ViewsConnector end views show the cavity or terminal locationsfor most connectors shown in the system schematic(s). Thedrawings show the connectors face as seen after the harnessconnector has been disconnected from a component or mat-ing connector. Unused cavities are left blank in the table.

In addition, the color and part number of the connectorbody are provided, along with the family/series name are oftenincluded, figure 1-29.

Circuit DescriptionsMost charts also have a circuit description (not shown in Fig.1-28) that describes how the system works electrically. The cir-cuit description also explains the communication and interac-tion of all components that affect the operation of the system.

For example: The Wheel Speed Sensor (WSS) coil emitsan electromagnetic field. A toothed ring on the wheel passesby the WSS and disrupts this electromagnetic field. The dis-ruption in the field causes the WSS to produce a sinusoidal(AC) voltage signal.

BATTERY SERVICE AND TESTINGBattery voltage that is out of specifications can have an adverseeffect on the electronic engine control system. If the voltage istoo low, actuators such as the fuel injectors may not open faror long enough to deliver the correct amount of fuel. As an op-posite effect, when battery voltage is too high the injectors mayopen too far or too long and deliver more than the designedamount of fuel to the engine. These conditions posed a prob-lem in the early years of electronic controls, but most modernsystems feature a voltage correction strategy that corrects forthe voltage variations.

Battery TestingState-of-charge and capacity tests are performed to determinethe condition of the battery. In addition, a preliminary evalu-ation on a low-maintenance or maintenance-free battery isrequired to determine if the battery is capable of accepting arecharge.

State-of-Charge TestingUntil the appearance of sealed, maintenance-free batteries,testing the specific gravity of the electrolyte with a hydrom-eter was a universal method of determining battery condi-tion. However, the procedure can be used today only on theminority of batteries that are unsealed and have removablefiller caps.

Some sealed maintenance-free batteries are equippedwith a built-in state-of-charge indicator in one cell. This in-dicator has two functions: It shows whether electrolyte hasfallen below a minimum level and also serves as a go/no-gohydrometer. The indicator is a plastic rod inserted in the topof the battery and extended into the electrolyte. One designuses a single plastic ball, usually colored green, red, or blue,suspended in a cage from the bottom of the rod, figure 1-30.Depending on the specific gravity of the electrolyte, the ballwill float or sink in its cage, changing the appearance of theindicator eye.

Generally, a green dot in the indicator means the batteryis charged enough for testing. If this dot is not visible, the bat-tery must be charged before it is tested. If the indicator eye isblack and color is not visible, the battery is below a 65 percent

Fig. 1-28. Typical component locator chart.



state-of-charge and must be recharged before testing. If theindicator is clear or light yellow, the electrolyte level has fallenbelow the bottom of the indicator rod and attached cage.When this clear or light yellow appearance is noted, lightly tapthe top of the indicator to dislodge any gas bubbles that mightbe giving a false indication of low electrolyte level. If the colordoes not change, replace the battery. Do not attempt torecharge a battery if the electrolyte level is too low.

Some battery indicators contain both a red and a greenball. This gives the indicator a green, dark, red, and clearappearance, in that order. The red dot indicates the battery is

approaching complete discharge and must be charged beforebeing used. Complete indicator information is printed on alabel attached to the battery and should be used to make anaccurate interpretation of the built-in indicator.

ABNORMAL OR PHANTOM BATTERY DRAIN PROBLEMSPhantom battery drain, or parasitic draw, is caused by some-thing in the vehicle constantly drawing current from the bat-tery when the ignition is off. Although a certain amount ofdischarge is normal and can be expected, a fully chargedbattery in good condition should not lose its charge when leftidle for a few days or even weeks. This loss of voltage can causedriveability problems if the draw is enough to cause the PCMto lose stored operational information. The loss of learnedvalues for any of the following systems may cause undesirableperformance issues:

Fuel trim values Ignition timing advance information Transmission shift points

Typical causes of battery drain include:

Acid, moisture, dirt, or corrosion on top of the battery case An accessory, such as a trunk light, glove box light, un-

derhood light, or cigarette lighter, remaining on when thevehicle is not in use

Fig. 1-29. Typical connector end view chart.

Fig. 1-30. Maintenance-free battery state-of-charge indicator.


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Parasitic drains required to operate systems that continueto work even when the vehicle is parked and the ignitionis off

The most serious of these are the parasitic losses resulting fromthe advent of computer controls. Virtually all late-model vehi-cles are equipped with computers that control such things asengine operation, radio tuning, suspension leveling, steeringassist, antilock brakes, and more. Each of these microproces-sors contain random access memory (RAM) that stores infor-mation relevant to its job. Remember: RAM requires a constantpower supply that puts a continuous drain on the vehicle elec-trical system. In addition, many electronic control systems con-duct a self-diagnostic test after the engine is switched off. Thecombined drain of several computer memories, or diagnostictest routines, can discharge a battery to the point where there isinsufficient cranking power after only a few weeks.

Due to the higher parasitic current drains on late modelvehicles, the old test of removing a battery cable connection andtapping it against the terminal while looking for a spark is bothdangerous and no longer a valid check for excessive currentdrain. Furthermore, every time the power source to computermodules is interrupted, module memories are lost. Informationprogrammed into memory by the vehicle owner, such as radiopresets, door lock combinations, seat position memories, andclimate controls, all have to be reset when the battery is recon-nected. On engine management systems with adaptive learningcapability, driveability also may be affected until the computerrelearns the engine calibration or transmission shift modifica-tions that were erased from memory.

A clean battery top prevents any drain from the negative topositive battery terminals. Periodically clean the battery top andterminals with a mixture of baking soda and water applied witha brush. Do not allow the solution to enter the battery cells.

To test for abnormal battery drain, disconnect the negativebattery cable and connect an ammeter in series between the neg-ative terminal and the cable, figure 1-31. On many late-modelvehicles it is necessary to wait up to one hour before taking the

reading. Many onboard computers have timer circuits whichmust time out before they shut down.

To isolate the source of a draw, disconnect each accessorysystem one at a time until the meter reading drops into thenormal range. This locates the offending circuit. Consult awiring diagram to determine how power is routed through thecircuit, then systematically eliminate components to deter-mine which one was remaining on and draining the battery.

STARTING SYSTEM SERVICEThe starting system includes the battery, ignition switch, safetyswitch, starter relay, solenoid, and starter motor, as well as thecircuitry that links everything together. A failure at any point ofthe system can prevent the engine from starting. When anengine fails to crank, perform these preliminary checks:

Inspect the batterycheck for loose, corroded, or dam-aged terminals and cable connections. Also check the bat-tery state-of-charge

Inspect the ignition switchcheck for loose mounting,damaged wiring, sticking contacts, and loose connections

Inspect the safety switchcheck for proper adjustment,loose mounting and connections, and damaged wiring

Inspect the solenoidcheck for loose mounting, looseconnections, and damaged wiring

Inspect the starter motorcheck for loose mounting,proper pinion adjustment, and loose or damaged wiring

If the system passes a visual inspection, perform current draw andcranking voltage tests to determine the general condition of thestarter motor. Begin by verifying that the battery is fully chargedand in good condition. While testing, the starter motor is crank-ing the engine; however, the engine must not start and run. Toprevent starting, either bypass the ignition switch with a remotestarter switch or disable the ignition. Do not crank the startermotor for more than 15 seconds at a time while testing. Allow twominutes between tests for the motor to cool and prevent damage.

Cranking Current Draw TestThe cranking current draw test measures the amount of cur-rent, in amperes, that the starter circuit requires to crank theengine. This test, which helps isolate the source of a startingproblem, is performed with either a charging-starter-battery(CSB) analyzer or individual voltmeter and inductive amme-ter. To test with inductive ammeter meter:

1. Bypass the ignition with a remote starter switch.2. Connect the voltmeter leads to the battery terminals,

observing correct polarity.3. Clamp the inductive ammeter pickup around the posi-

tive cable.4. Crank the engine for several seconds and note the volt-

meter and ammeter readings, figure 1-32.5. Compare ammeter readings to specifications.

With a CSB analyzer, connect the leads and test according to theequipment instructions. Regardless of method, high currentdraw is caused by a short in the starter circuit or a bindingstarter motor or engine. Low current draw results from highresistance in the starting system circuit or an undercharged ordefective battery.Fig. 1-31. Connection for testing for parasitic draw.



High resistance in the cranking circuit can cause eitherhigh or low current draw. This is because the starter motor re-quires high current to get up to speed. Once up to speed, thestarter motor acts like a generator to produce a counter volt-age that limits the current. Because the motor requires highcurrent when turning slowly, high resistance can prevent astarter from getting enough current to get up to speed. As a re-sult, the motor turns slowly and does not limit the current.

If resistance is high enough, it limits current to the starter,which causes the starter motor to turn slowly or not at all. Highresistance can be seen on the ammeter when the starter is firstengaged. If current momentarily goes high, then settles downto a lower amount, suspect high resistance.

When high resistance is indicated, perform starter circuitresistance tests. If testing indicates a starter motor problem, re-move the unit for service.

Cranking Voltage TestThis test, which measures available voltage at the starter dur-ing cranking, is performed to check for high resistance in thestarter circuit. Test results are read on a voltmeter. To test:

1. Bypass the ignition switch with a remote starter switch.2. Connect the negative voltmeter lead to a good ground

and connect the positive voltmeter

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